Influence of ligation method on friction resistance of lingual
brackets with different second-order angulations: an in vitro study
Graziane Olímpio Pereira1, Carla Maria Melleiro Gimenez2, Lucas Prieto3, Marcos Gabriel do Lago Prieto4, Roberta Tarkany Basting5
Objective: To evaluate stainless steel archwire static friction in active and passive self-ligating lingual and conventional brackets with second-order angulations. Methods: Two conventional lingual brackets for canines (STb light/Ormco; PSWb/Tecnident), and two self-ligating brack-ets, one active (In-Ovation L/GAC) and the other passive (3D/ Forestadent), were evaluated. A stainless steel archwire was used at 0°, 3° and 5° angulations. Metal ligatures, conventional elastic ligatures, and low friction elastic ligatures were also tested. A universal testing machine applied friction between brackets and wires, simulating sliding mechanics, to produce 2-mm sliding at 3 mm/minute speed. Results: Two-way analysis of variance demonstrated a significant effect of the interaction between brackets and angulations (p < 0.001). Tukey test indicated that the highest frictional resistance values were observed at 5° angulation for In-Ovation L, PSWb bracket with non conventional ligature, and STb bracket with metal ligature. As for 3D, PSWb with conventional or metal ligatures, and STb brackets with non conventional ligature, showed significantly lower static frictional resistance with 0° angulation. At 0° angulation, STb brackets with metal ties, In-Ovation L brackets and 3D brackets had the lowest frictional resistance. Conclusions: As the angulation increased from 0° to 3°, static friction resistance increased. When angulation in-creased from 3° to 5°, static friction resistance inin-creased or remained the same. Self-ligating 3D and In-Ovation L brackets, as well as conventional STb brackets, seem to be the best option when sliding mechanics is used to perform lingual orthodontic treatment.
Keywords: Friction. Ligation. Orthodontic brackets.
1 Research Assistant, São Leopoldo Mandic, Department of Dental Material and Restorative Dentistry, School of Dentistry and Research Institute, Campinas, São Paulo, Brazil.
2 Professor, Universidade de Araras (UNIARARAS), Department of Orthodontics, Araras, São Paulo Brazil. Universidade Estadual Paulista (FOA-UNESP), School of Dentistry, Department of Orthodontics, Araraquara, São Paulo, Brazil.
3 Private practice, Campo Grande, Mato Grosso do Sul, Brazil. 4 Professor, São Leopoldo Mandic, Department of Dental Material and
Restorative Dentistry, School of Dentistry and Research Institute, Campinas, São Paulo, Brazil.
Submitted: February 20, 2015 - Revised and accepted: January 18, 2016 DOI: http://dx.doi.org/10.1590/2177-6709.21.4.034-040.oar
How to cite this article: Pereira GO, Gimenez CMM, Prieto L, Prieto MGL, Basting RT. Influence of ligation method on friction resistance of lingual brackets with different second-order angulations: an in vitro study. Dental Press J Orthod. 2016 July-Aug;21(4):34-40.
DOI: http://dx.doi.org/10.1590/2177-6709.21.4.034-040.oar
» The authors report no commercial, proprietary or financial interest in the products or companies described in this article.
Contact address: Graziane Olimpio Pereira Avenida Senador Lemos 435 - Sala 403 CEP 66050-000 Belém - PA - Brazil E-mail: graziane.orto@icloud.com
Objetivo: avaliar o atrito estático de fios de aço inoxidável em braquetes linguais autoligáveis ativos e passivos, e braquetes linguais ligados con-vencionalmente, com angulações de segunda ordem. Métodos: dois tipos de braquetes linguais convencionais para caninos (STb light, Ormco, e PSWb, Tecnident) e dois tipos de braquetes autoligáveis, um ativo (In-Ovation L, GAC) e outro passivo (3D, Forestadent), foram avaliados. Um fio de aço inoxidável com angulações de 0°, 3° e 5° foi utilizado. Ligaduras metálicas, elásticas convencionais e ligaduras elásticas de baixo atrito também foram testadas. Uma máquina de ensaio universal causou atrito entre os braquetes e os fios, simulando uma mecânica de desliza-mento de 2mm, a uma velocidade de 3mm/minuto. Resultados: a análise de variância de dois níveis demonstrou haver um efeito significativo resultante da interação entre braquetes e angulações (p < 0,001). O teste de Tukey indicou que os valores mais altos de resistência ao atrito foram observados com uma angulação de 5° no braquete In-Ovation L, e no braquete STb com ligadura metálica. Já os braquetes 3D e In-Ovation L, e os braquetes STb com ligadura não convencional apresentaram valores de resistência ao atrito significativamente baixos com uma angulação de 0°. Com angulação de 0°, os braquetes STb com ligaduras metálicas, braquetes In-Ovation L e braquetes 3D apresentaram os mais baixos valores de resistência ao atrito. Conclusões: à medida que a angulação aumentou de 0° para 3°, a resistência ao atrito estático também aumentou. À me-dida que a angulação aumentou de 3° para 5°, a resistência ao atrito estático também aumentou ou continuou a mesma. Os braquetes autoligáveis 3D e In-Ovation L, assim como os braquetes convencionais STb, parecem ser as melhores opções quando a mecânica de deslizamento é usada no tratamento ortodôntico lingual.
INTRODUCTION
Lingual brackets are diferent from labial brackets in regard to coniguration and clinical aspects. Specii-cally, conventional lingual brackets are smaller sized to
increase patient’s comfort and improve oral hygiene.1
Almost all lingual brackets are single and have narrower mesiodistal width than buccal brackets because of their anatomical limitations, and because they were projected to provide greater interbracket distance, despite being
more susceptible to tipping under traction force.2
Me-chanics work by means of sliding and have the advan-tage of minimizing the time of closing arch gaps and of reducing the number of activations; however, if teeth are not leveled properly, the increased friction between arches and brackets can generate unexpected dental
movements and greater anchorage loss.2
Some factors inluencing friction resistance are re-lated to the material composing brackets and wires, surface conditions of arches and bracket slot, archwire cross-section, torque at the wire-bracket interface, bonding strength, use of self-ligating brackets, inter-bracket distance, presence of saliva and inluence of
oral functions.3 In vitro studies have evaluated friction
resistance among diferent alloys and wire calibers by means of several ligation methods and material of buc-cal orthodontic brackets with alterations in angula-tion, using models with one, three, ive and ten
brack-ets, and typodonts to simulate diferent situations.4-10
However, few studies on friction produced by lingual
brackets have been published.2,11,12
When the angle between the bracket and the arch (second-order angle) increases, frictional resistance (more speciically, binding) appears to increase quickly, and even more quickly beyond the critical contact
an-gle.2 If the arch does not bend (i.e., deform elastically),
the angle will not increase beyond the critical contact angle, but sometimes there is sliding resistance and some
amount of retraction force is lost.2,11 In this context, it
becomes interesting to evaluate static friction resistance of diferent lingual bracket types (conventional and self-ligating) at diferent angulations.
MATERIAL AND METHODS
The experimental units were composed of stainless steel brackets of diferent commercial brands evaluated with a single-diameter rectangular wire submitted to
friction at diferent angles (n = 5).2,9 The material used
in the experimental units and their respective character-istics and manufacturers are shown in Table 1. Brackets used are shown in Figure 1.
Acrylic cylindrical devices were developed for bracket bonding and positioning of angulations to conduct the friction resistance tests. At one end of the device, an L-shaped steel key was manufactured and inserted through a mechanical lathe to ensure the key would not become dislocated within the acrylic device when posi-tioning the second-order angulation. At the other end, bracket bonding was performed for subsequent evalua-tion. The devices were engaged in a prefabricated metal apparatus screwed onto the base of the universal testing
Figure 1 - Brackets used in the study: A) PSWb (Tecnident, São Carlos/SP, Brazil); B) STb light (Ormco, USA); C) In-Ovation L (GAC, USA); D) 3D (Forestadent, Germany).
machine (Emic DL 2000, São José dos Pinhais, Paraná, Brazil) in order to carry out the friction trials (Fig 2). For evaluation of bracket positioning in second-order angulation, a plastic Protractor (KJIN, plastic, 180 de-grees, Shenzhen, Guangdong, China) was adapted to the metal apparatus to measure the angles (Fig 2).
The metal wire (0.016 x 0.022-in) (Ortho Organizers) to be pulled was cut 10-cm in length and used as a guide to standardize the positioning of the bracket bonded to the acrylic device. The following bonding procedure was used. Brackets were inserted 10 mm from one end of the wire, while the other end of the wire was inserted 10 mm into the load cell coupled to the universal testing machine for standardization purposes. In doing so, the face of the bonded bracket
Material Characteristics Manufacturer (city, state, country)
Prieto Straight Wire/ PSWb
0.018 x 0.030-in slot
Tecnident (São Carlos, São Paulo, Brazil) Maxillary canines R/L
Torque: 55°; angulation: 9°; distal ofset: 8°
Conventional
STb
0.018 x 0.025-in slot
Ormco (Glendora, CA, USA) Maxillary incisors and canines R/L
-ref. 369-2102
Torque: 55°; angulation: 0°; rotation: 0°
Conventional
In-Ovation L
0.018 x 0.025-in slot
GAC (Bohemia, NY, USA) Maxillary Canines R/L - ref. 190-531-00
Torque: 60°; angulation: 0°; rotation: 0°
Active self-ligating
3D
0.018 x 0.025-in slot
Forestadent (Pforzheim, Baden-Württemberg,
Germany) Maxillary incisors and canines R/L
-ref. 707-0033
Torque: 45°, angulation: 0°; rotation: 0°
Passive self-ligating
Easy-To-Tie clear ligature
Conventional elastomers without latex,
with 45° curvature 3M Unitek (Monrovia, CA, USA)
(ref. 406-870)
Super-Slick clear ligature Low friction non conventional elastomers TP Orthodontics (La Porte, IN, USA) (ref. 382-921)
Stainless steel wire 0.016 x 0.022-in (ref. 100047) Ortho Organizers (Carlsbad, CA, USA)
Metal ligature 0.010-in (ML) (ref. 55.01.210) Morelli (Sorocaba, São São Paulo, Brazil)
Table 1 - Characteristics of material used in the experiment.
remained parallel to the edge of the acrylic device, so as to prevent interference from torque and angulation. Fast curing glue (Super Bonder GEL, Henkel, Itapevi, SP, Brazil) was applied to the base of the bracket already attached to the wire in the load cell, according to the connection method to be studied. The metal apparatus screw holding the test specimen was loosened and then inserted tightly against the base of the bracket, taking care not to alter anything, and to retain the bracket-wire set in a “passive coniguration.”
After bonding each bracket to be tested, the brack-ets were tied to the wire with different types of liga-tures: conventional brackets (STb, PSWb) were tied with conventional ligatures (Easy-To-Tie), non con-ventional were tied with low-friction (Super Slick) and metal ligatures, and the clip on the self-ligating active (In-Ovation L) and passive (3D) lingual brack-ets set was locked into place.
Friction resistance tests were performed at room temperature (24 °C) by applying a drop of artificial
saliva13 (3.5 g porcine mucin; 2 g xylitol; 100 mg
metilparabene; 50 mg EDTA; 2 mg benzalkonium chloride; 0.42 mg sodium fluoride; 100 ml aqueous solution) to simulate lubrication of the oral environ-ment. Before starting each test, artificial saliva was applied with a micropipette (HTL Labmate, Danisze-wska, Warsaw, Poland) by dripping the solution into the slot of the bracket (Fig 2).
The friction resistance test was performed ive times for each one of the established angulations (0°, 3° and 5°). At each repetition, elastomeric and metal ligatures were replaced on conventional brackets. In testing the self-ligating brackets, the machine was repositioned to the initial position, and the clip was opened and closed. Each time the test was performed, artiicial saliva was placed in the slot of the bracket to be tested, and the whole bracket-wire set was wiped with cotton soaked in 70% alcohol.
Initially, the tests were carried out with 0° angula-tion for a given type of bracket. Subsequently, a new bracket-wire set was positioned in the acrylic device and the load cell, respectively, in accordance with the procedures previously described. To position the bracket in the desired angulation, the screw of the metal apparatus that positions the device was loosened with the appropriate key. The L-shaped steel key of the acrylic device was rotated manually to reach the
desired angulation of the bracket-wire set, at 3° or 5°, using a protractor as reference. The bracket-wire set was repositioned at 0° angulation before performing each 3° and 5° angulation test.
The universal testing machine was programmed to pull the wire at a speed of 3 mm per minute, with 2 mm of wire displacement by the bracket slot. Friction resis-tance generated during wire movement was determined with a load cell of 50 N coupled to a universal testing machine. The universal testing machine and a sotware application (Tesc version 3.01, São José dos Pinhais, Paraná, Brazil) were used to apply sliding and friction resistance between brackets and wire. Canine distal sliding resistance was simulated from the right side of a 0.016 x 0.022-in wire in a previously aligned arch.
Before data analyses, normality of distribution and homogeneity of variance of values were checked by means of Shapiro-Wilk and Levene tests, and so was the presence of discrepant data. Normal distribution of data was observed and two-way analysis of variance was em-ployed. Tukey test was carried out to perform multiple comparisons. SPSS sotware 20 (SPSS Inc., Chicago, IL, USA) was used to perform statistical calculations, adopting a signiicance level of 5%.
RESULTS
The two-way analysis of variance showed a sig-nificant effect of the interaction between brackets and angle factors (p < 0.001). Tukey test showed that there was no significant difference in static friction generated by the evaluated brackets-ligatures for the test condition without angulation (0°).
The passive self-ligating system (3D) generated fric-tion values that were not significantly different from those observed with the active self-ligating bracket system (In-Ovation L). The conventional PSWb system associated with conventional ligation result-ed in statistically higher friction, comparresult-ed with the passive self-ligating bracket (3D).
Under 5° angulation, there was no significant dif-ference in friction force values provided by PSWb brackets with metal or conventional ligature, STb brackets with unconventional ligature and passive 3D self-ligating brackets. The highest static friction values were recorded for In-Ovation L brackets and associated non conventional PSWb ligature, which, in turn, did not differ significantly from STb bracket with metal ligature.
Tukey test indicated that the least friction force was measured in the absence of angulation, whereas the highest values were observed in 5° angulation for the active self-ligating bracket (In-Ovation L), con-ventional PSWb with unconcon-ventional ligature, and STb with metal ligature. Static friction force for the passive self-ligating system (3D), PSWb conven-tional brackets with convenconven-tional or metal ligatures, and STb brackets associated with an unconventional ligature, were significantly lower at an angle of 0°, but there was no significant difference between friction values generated with 3° and 5° angulations.
Only STb bracket with metal ligature showed no difference in friction force at 0° and 3° angles. The highest friction force for the STb bracket was ob-served in 5° angulation.
DISCUSSION
As regards the method of bracket ligation, the pres-ent study showed no statistically signiicant diferences at 0° angulation. However, several studies with labial brackets and the few existing studies with lingual brack-ets showed that increasing reduction or friction de-pended on the ligation method using passive or active self-ligating brackets, conventional or unconventional elastomeric ligatures, metal ligature types, and diferent
wires alloys and gauges.5,8-12,14-18
Super Slick ligatures have been thought to reduce friction because of their Metaix coating which reduces
friction and adhesion of residues and plaque.19
Howev-er, in the present research, these ligatures did not cause less friction, corroborating the indings of other stud-ies14,20,21,22 which evaluated diferent kinds of elastic liga-tures, including Easy-to-Tie and Super Slick. The latter showed the least resistance to friction, while the former showed the smallest values; however, metal ligatures and self-ligating methods were not compared. On the other
hand, other studies4,20,23 showed greater friction than
that of self-ligating brackets and metal ligatures.
Other studies have shown that elastic Super Slick reduced friction resistance, compared with other
con-ventional elastic ligatures, including Easy-to-Tie,4,24
not corroborating the results of this study. Hain et al4
observed that Super Slick ligatures increased friction by 80% when not immersed in human saliva. For this rea-son, artiicial saliva lubrication was used in this study.
Leanderand and Kumar19 reported that Metaix is a
hy-drophobic coating and becomes slippery in the presence of water or saliva, thus reducing friction.
Table 2 - Mean and standard deviations in gf of static friction force, according to bracket type and angulation.
CL: Conventional Ligature; ML: Metal Ligature; NCL: Non Conventional Low Friction Ligature. Means followed by different superscript capital letters indicate sig-nificant difference among brackets–ligatures, considering each angulation individually (comparisons within each column). Mean followed by distinct superscript lowercase letters indicate significant difference among angles, considering each individual bracket-ligature (comparisons within each line).
Bracket – Ligature 0o 3o 5o
3D 18 ± 4 Aa 408
± 38 CDb 516
± 25 ABCb
In-Ovation L 10 ± 7 Aa 292
± 87 BCb 682
± 110 Dc
PSWb – CL 56 ± 5 Aa 610
± 139 Eb 488
± 75 ABCb
PSWb – ML 120 ± 66 Aa 328
± 131 Cb 376
± 64 Ab
PSWb – NCL 46 ± 22 Aa 476
± 35 DEb 684
± 47 Dc
STb – CL 30 ± 7 Aa 132
± 55 Aa 530
± 45 BCb
STb – ML 0 ± 0 Aa 164
± 48 ABb 632
± 86 CDc
STb – NCL 90 ± 12 Aa 322
± 41 Cb 412
Thorstenson and Kusy25 reported the importance of observing the critical angle, i.e., the angle in which the wire touches the opposite corners of the bracket. At this point, friction increases significantly with any type of bracket and wire, and when the arch does not deform beyond the critical angle (known as bind-ing), sliding resistance occurs and some portion of the retraction force is lost. The present study showed that increased angulation led to increased resistance to friction, corroborating the findings of other
au-thors who have studied labial and lingual braces.2,11,25.
The choice of 0°, 3° and 5° angulations for this re-search protocol was based on previous studies
avail-able in the literature.2,11,25 More specifically, the
findings of Park et al2 described the critical angle as
ranging between 1° and 3° when using lingual braces in second-order angulations with 0.018 x 0.025-in slots and coupled to 0.016 x 0.022-in stainless steel wires. Therefore, angulations greater than 5° were not needed to evaluate canine retraction. In addition, orthodontic dental movement is not continuous and linear, but rather dynamic and discontinuous; that is
why second-order angulations must be evaluated.2,11,25
Ortan et al11 reported that the ideal wire for partial
canine retraction would be a 0.016 x 0.016-in stainless steel wire, and the ideal wire for mass retraction would be a 0.016 x 0.022-in stainless steel wire. Partial canine retraction becomes infeasible in lingual orthodontic treatment because patient’s esthetics would be com-promised, and the patient opted for this mode of treat-ment due to its good esthetic results. Therefore, mass retraction would be the best choice. However, no in vi-tro model has been reported up to date, which could reproduce this research performed by retracting the six
anterior teeth.2,11
For maximum anchorage cases, low-friction brack-ets seem to be the most efective alternative in posterior
segments when sliding mechanics is used.11 In lingual
Orthodontics, low-friction brackets may increase the risk of mesiobuccal molar rotation, distobuccal canine rotation and expansion of the arch, causing a transverse
bowing efect.2,11 The brackets with elastic ligatures
and PSWb brackets with metal ligature presented the highest resistance to static friction, probably due to their deep slot design, and may ofer clinical signiicance. However, friction-related studies on lingual brackets
are still too few to make comparative conclusions,2,12
although Lalithapriya et al12 showed that self-ligating
brackets may not be beneicial in reducing friction dur-ing en-mass retraction due to their interactive clip type. In 3° angulation, STb brackets with conventional ligatures had the least resistance to friction and showed no statistically signiicant diference between 0° and 3° angulations, a situation in which STb bracket with metal ligature performed similarly. This can be ex-plained by the variation in the critical contact angle
between 1° and 3° with 0.016 x 0.022-in wires.2
De-spite the reduced static friction resistance of this group, in comparison with the other groups, this cannot be considered a positive factor for lingual brackets, since the same feature also acts as a negative factor, owing to
reduced control ofered by a single bracket.2,11 In
gen-eral, resistance to static friction increased signiicantly when the angulation increased to 3° and 5°,
corrobo-rating previous studies.2,11,25
In lingual orthodontic treatment in which lower resistance to friction is required, self-ligating brackets (3D, In-Ovation L) and conventional brackets (STb) with metal ligatures appear to be the best treatment option. Although this study has some limitations due to the characteristics of an in vitro trial, such as over controlled variables, number of specimens per group and diferences in slot designs among brackets, the results of this current research could inluence and guide orthodontists who prefer to use lingual brackets
in their clinical practice. The studies by Ortan et al11
found lower friction force with In-Ovation L brack-ets, compared with the conventional brackets evalu-ated in this research, corroborating the indings of our research. Self-ligating brackets have the advantage of providing shorter chair time, in comparison with
metal ligatures, because they are easier to handleand
minimize the risk of a metallic washer tip escaping during eating or brushing, an event that could hurt
patient’s tongue.11 Although PSWb brackets have a
0.018 x 0.030-in slot, they showed no reduced friction resistance related to greater depth, in comparison with the other brackets evaluated in this experiment, prob-ably due to some irregularities in the slot, which could inluence friction. However, scanning electron micro-scopic evaluations should be taken to conirm this
hy-pothesis. Ortan et al11 evaluated the slot dimensions of
the manufacturers did not match those of the research results, and that all brackets had larger dimensions. The signiicance of these indings is that lower friction can be induced by a larger slot size, and this could cause problems of second and third orders, by
compromis-ing torque and rotation control.11 Therefore, the use of
0.022-in slot brackets could also provide lower friction resistance when using 0° angulation due to a large slot design that may result in a gap between the archwire and the bracket; however, an increase in angulation produces higher friction.
CONCLUSIONS
In spite of the limitations of this in vitro study, some conclusions can be drawn, as follows:
- When angulation increased from 0° to 3°, static friction resistance increased. When angulation
in-creased from 3° to 5°, static friction resistance increased
or remained the same.
- Self-ligating 3D and In-Ovation L brackets, as well as conventional STb brackets, seem to be the best op-tion when sliding mechanics is used to perform lingual orthodontic treatment.
REFERENCES
1. Geron S. Self-ligating brackets in lingual orthodontics. Semin Orthod. 2008;14(1):64-72.
2. Park JH, Lee YK, Lim BS, Kim CW. Frictional forces between lingual brackets and archwires measured by a friction tester. Angle Orthod. 2004 Dec;74(6):816-24. 3. Cacciafesta V, Sfondrini MF, Ricciardi A, Scribante A, Klersy C, Auricchio F.
Evaluation of friction of stainless steel and esthetic self-ligating brackets in various bracket-archwire combinations. Am J Orthod Dentofacial Orthop. 2003 Oct;124(4):395-402.
4. Hain M, Dhopatkar A, Rock P. A comparison of diferent ligation methods on friction. Am J Orthod Dentofacial Orthop. 2006 Nov;130(5):666-70. 5. Matarese G, Nucera R, Militi A, Mazza M, Portelli M, Festa F, et al. Evaluation
of frictional forces during dental alignment: an experimental model with 3 nonleveled brackets. Am J Orthod Dentofacial Orthop. 2008 May;133(5):708-15. 6. Gandini P, Orsi L, Bertoncini C, Massironi S, Franchi L. In vitro frictional
forces generated by three diferent ligation methods. Angle Orthod. 2008 Sept;78(5):917-21.
7. Baccetti T, Franchi L, Camporesi M, Defraia E, Barbato E. Forces produced by diferent nonconventional bracket or ligature systems during alignment of apically displaced teeth. Angle Orthod. 2009 May;79(3):533-9.
8. Tecco S, Tetè S, Festa F. Friction between archwires of diferent sizes, cross-section and alloy and brackets ligated with low-friction or conventional ligatures. Angle Orthod. 2009 Jan;79(1):111-6.
9. Heo W, Baek SH. Friction properties according to vertical and horizontal tooth displacement and bracket type during initial leveling and alignment. Angle Orthod. 2011 July;81(4):653-61.
10. Leite VV, Lopes MB, Gonini Júnior A, Almeida MR, Moura SK, Almeida RR. Comparison of frictional resistance between self-ligating and conventional brackets tied with elastomeric and metal ligature in orthodontic archwires. Dental Press J Orthod. 2014 May-Jun;19(3):114-9.
11. Ozturk Ortan Y, Yurdakuloglu Arslan T, Aydemir B. A comparative in vitro study of frictional resistance between lingual brackets and stainless steel archwires. Eur J Orthod. 2012 Feb;34(1):119-25.
12. Lalithapriya S, Kumaran NK, Rajasigamani K. In vitro assessment of competency for diferent lingual brackets in sliding mechanics. J Orthod Sci. 2015 Jan-Mar;4(1):19-25.
13. Christersson CE, Lindh L, Arnebrant T. Film-forming properties and viscosities of saliva substitutes and human whole saliva. Eur J Oral Sci. 2000 Oct;108(5):418-25. 14. Tecco S, Di Iorio D, Cordasco G, Verrocchi I, Festa F. An in vitro investigation
of the inluence of self-ligating brackets, low friction ligatures, and archwire on frictional resistance. Eur J Orthod. 2007 Aug;29(4):390-7.
15. Arun AV, Vaz AC. Frictional characteristics of the newer orthodontic elastomeric ligatures. Indian J Dent Res. 2011 Jan-Feb;22(1):95-9.
16. Tecco S, Di Iorio D, Nucera R, Di Bisceglie B, Cordasco G, Festa F. Evaluation of the friction of self-ligating and conventional bracket systems. Eur J Dent. 2011 July;5(3):310-7.
17. Huang TH, Luk HS, Hsu YC, Kao CT. An in vitro comparison of the frictional forces between archwires and self-ligating brackets of passive and active types. Eur J Orthod. 2012 Oct;34(5):625-32.
18. Montasser MA, El-Bialy T, Keilig L, Reimann S, Jäger A, Bourauel C. Force levels in complex tooth alignment with conventional and self-ligating brackets. Am J Orthod Dentofacial Orthop. 2013 Apr;143(4):507-14.
19. Leander D, Kumar JK. Comparative evaluation of frictional characteristics of coated low friction ligatures - Super Slick Ties with conventional uncoated ligatures. Indian J Dent Res. 2011 Jan-Feb;22(1):90-4.
20. Griiths HS, Sherrif M, Ireland AJ. Resistance to sliding with 3 types of elastomeric modules. Am J Orthod Dentofacial Orthop. 2005 Jun;127(6):670-5; quiz 754.
21. Crawford NL, McCarthy C, Murphy TC, Benson PE. Physical properties of conventional and Super Slick elastomeric ligatures after intraoral use. Angle Orthod. 2010 Jan;80(1):175-81.
22. Cunha AC, Marquezan M, Freitas AOA, Nojima LI. Frictional resistance of orthodontic wires tied with 3 types of elastomeric ligatures. Braz Oral Res. 2011;25(6):526-30.
23. Khambay B, Millett D, McHugh S. Evaluation of methods of archwire ligation on frictional resistance. Eur J Orthod. 2004 Jun;26(3):327-32.
24. Hain M, Dhopatkar A, Rock P. The efect of ligation method on friction in sliding mechanics. Am J Orthod Dentofacial Orthop. 2003 Apr;123(4):416-22. 25. Thorstenson GA, Kusy RP. Efect of archwire size and material on the resistance
